This module is intended to test your regular expressions.  Given a
subject string and a regular expression (aka pattern), the module
not only tests whether the regular expression complete matches the
subject string, it performs a utf8::upgrade or utf8::downgrade on
the subject string and performs the tests again, if necessary.
Furthermore, given a pattern with capturing parenthesis, it checks
whether all captures are present, and in the right order.  Both
named and unnamed captures are checked.
